With the rapid economic growth, circulation amount of the paper money become larger and larger, and therefore the traditional way of manual handling in the bank could hardly meet the requirements of handling large amount of paper money. To improve the efficiency of paper money handling and reduce labor costs, there is an urgent need to put a large amount of usable and reliable financial self-service equipments into market. However, a high proportion of the paper money in circulation are old paper money, and the image of most old paper money are degraded by handwriting, scratches, stain, folds, which make paper money identification more difficult. Since the present, the financial self-service equipments produced by the domestic and foreign manufacturers have poor adaptability for the damaged paper money and the old paper money, the financial self-service equipments put into the market present high paper money refusal rate and poor usability, and therefore impairing the popularization of the financial self-service equipments. If the image quality of the old paper money could be restored to that of the new paper money, it is possible to solve the problem that the financial self-service equipments have the high paper money refusal rate for the old paper money. At present, the image restoration technique based on the partial differential equation has get some progress, and can get well restoring performance when it is used to handle the degradation like scratches, handwriting, stain and folds. The studying contents of the image restoration based on the partial differential equation and image restoration of the old paper money are consistent. Therefore, it is possible to achieve well restoration performance by applying image restoration technique based on the partial differential equation to the image restoration of the bank note.
FIG. 1 is a flow chart showing the traditional bank note image identification processing. As shown, at first, the whole image is processed for image restoration to extract its features, then the bank note is classified according to the standards such as bank note type, denomination and new or old degree, and finally the bank note is identified.
T is designated as the identifying time for each bank note, ta is designated as the time for image processing, tb is designated as the time for feature extracting, ta is designated as the time for classifying, td is designated as the time for identifying, Tmax is designated as the time range for the real-time response of the system. When and only when the identifying system satisfies equation (1), the requirements for the practical application could be reached:T=ta+tb+tc+td T≦Tmax  (1)
For the old bank note which is degraded by handwriting, scratches, stain, folds, the degradation of the bank note will reduce the identification accuracy of the system. Under such circumstance, the system is firstly required to process the “whole image” of the bank note for image restoration, which will cost a lot of time, such that the image processing time ta become far greater than the classifying time tc, i.e. ta>>tc.
However, when applying bank note identifying system to financial self-service equipments, high real-time performance is required in which identification for each bank note has to be finished in limited time period. In the bank note identifying system of prior art, the “whole image” of the bank note is firstly processed for image restoration in identification procedure, which cost a large amount of time; furthermore, the bank note having good image quality is also processed for image restoration in prior art, which wastes the system resources. The identifying time for each bank note is increased sharply, such that the bank note identifying system could hardly meet the requirements of real-time Tmax, as specifically shown in equation (2):
                                                                                                              T                    ↑                                    =                                                                                    t                        a                                            ↑                                              +                                                  t                          b                                                                                      +                                          t                      c                                        +                                          t                      d                                                                                                                                                                t                    a                                    >                                                            T                      max                                        -                                          (                                                                        t                          b                                                +                                                  t                          c                                                +                                                  t                          d                                                                    )                                                                                                    }                ⇒                  T          >                      T            max                                              (        2        )            
Therefore, existing bank note identifying system refuse to process the old bank note, i.e. refuse to identify the old bank note, in order to improve the real-time responding speed, such that a large amount of old bank notes are rejected and the bank note refusal rate of the bank note identifying system is high, which affect the usability of the bank note identifying system as well as the popularity of the financial self-service equipments adversely.